The present invention relates to a wiring material of semiconductor devices. Specifically the present invention relates to a semiconductor device having a circuit comprising a thin film transistor (hereinafter referred to as TFT), and a manufacturing method thereof. For example, the present invention relates to an electro-optical device, which is represented by a liquid crystal display panel, and an electronic device with an electro-optical device loaded as a component.
In this specification, a semiconductor device indicates general devices that can function by using semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic devices are all categorized as semiconductor devices.
Recently, techniques for using semiconductor thin films (with a thickness of about several nm to several hundreds of nm) formed over a substrate having an insulating surface to constitute a thin film transistor (TFT) have been in the spotlight. Thin film transistors are widely applied to electronic devices such as ICs and electro-optical devices, and the development thereof as switching elements for image display devices is hastened.
Conventionally, aluminum films formed by sputtering and having low resistivity have been often used as the wiring material for the above stated TFTs. However, when a TFT is manufactured by using aluminum as a wiring material, operation error or deterioration of TFT characteristics were caused by formation of projections such as hillocks or whiskers or by diffusion of aluminum atoms into the channel forming region, in the heat treatment.
As stated above, aluminum is not a preferable wiring material in the TFT manufacturing process because of its low heat resistance.
Therefore, materials comprising, for example, tantalum (Ta) or titanium (Ti) as a main component are being tested for use as a wiring material other than aluminum. Tantalum and titanium have a high heat resistance in comparison to aluminum, but on the other hand there arises a problem of high electrical resistivity. Further, if tantalum is performed with heat treatment at a temperature of about 500xc2x0 C., it becomes a problem that the electrical resistance increases by several times in comparison with that before heat treatment.
Furthermore, in the case that a film formed on a substrate possesses a large stress, substrate warping and film peeling generate, so it is preferable to perform film stress control and to form a film which possesses as low a stress as possible for a film formed by sputtering. As one means of controlling film stress, the use of a mixed gas of argon (Ar), krypton (Kr), xenon (Xe) as a sputtering gas has been proposed. However, since krypton (Kr) and xenon (Xe) are expensive, it is unsuitable for cases of mass production to use the mixed gas.
The present invention is accomplished in view of the above stated problems. The object of the present invention is to provide an electro-optical device having high reliability by using a material which has sufficiently low electrical resistivity, and sufficiently high heat resistance, as a wiring or as an electrode of respective circuits in the electro-optical device, typically an AM-LCD, and method of manufacturing thereof.
The structure of the present invention disclosed in this specification relates to a wiring material comprising tungsten or a tungsten compound as a main component, characterized in that argon is contained in an inert element within the wiring material at an amount of 90% or more, and the amount of sodium contained within the wiring material is 0.3 ppm or less.
In the above structure, the tungsten compound is a compound between a kind or a plural kinds of elements selected from the group consisting of Ta, Ti, Mo, Cr, Nb, and Si, and tungsten.
Further, the electrical resistivity of the wiring material in the above structure is 40 xcexcxcexa9xc2x7cm or less, preferably 20 xcexcxcexa9xc2x7cm or less.
Further, the structure of another invention relates to a semiconductor device having a wiring made from a metallic film containing a kind or a plural kinds of elements selected from the group consisting of W, Ta, Ti, Mo, Cr, Nb, and Si, a metallic compound film comprising said elements as main components; an alloy film of a combination of said elements; or a lamination film of thin films selected from the group consisting of said metallic film, said metallic compound film and said alloy film, characterized in that the wiring includes argon in an inert element within the wiring at 90% or more, and the amount of sodium contained within the wiring is 0.3 ppm or less.
Furthermore, the structure of another invention relates to a semiconductor device provided with a wiring containing a film comprising tungsten or a tungsten compound as a main component, characterized in that the wiring includes argon in an inert element within the wiring at an amount of 90% or more, and the amount of sodium contained within the wiring is 0.3 ppm or less.
Still further, the structure of another invention relates to a semiconductor device provided with a wiring having a lamination structure containing a film comprising tungsten or a tungsten compound as a main component, and a nitride film of tungsten, characterized in that the wiring includes argon in an inert element within the wiring material at an amount of 90% or more, and the amount of sodium contained within the wiring material is 0.3 ppm or less.
In addition, the structure of another invention relates to a semiconductor device provided with a wiring having a lamination structure including a silicon film having an added impurity element for imparting conductivity, a film comprising tungsten or a tungsten compound as a main component, and a nitride film of tungsten, characterized in that the wiring includes argon in an inert element within the wiring at an amount of 90% or more, and the amount of sodium contained within the wiring is 0.3 ppm or less.
In each of the above structures, the wiring is characterized by being formed by sputtering using argon as a sputtering gas.
In each of the above structures, an inert element other than argon (Xe or Kr) is characterized by being contained within the wiring at an amount of 1 atoms % or less. preferably, 0.1 atoms % or less.
Furthermore, any one of the above respective structures is characterized in that the internal stress of the tungsten film or the film comprising the tungsten compound as its main component is from xe2x88x922xc3x971010 dyn/cm2 to 2xc3x971010 dyn/cm2, preferably, xe2x88x921xc3x971010 dyn/cm2 to 1xc3x971010 dyn/cm2.
In addition, any one of the above respective structures is characterized in that the line width of the wiring is 5 xcexcm or less.
Further, any one of the above respective structures is characterized in that the film thickness of the wiring is 0.1 xcexcm or more, and 0.7 xcexcm or less.
Still further, any one of the above respective structures is characterized in that the wiring is used as a gate wiring of a TFT.
The structure of the present invention for realizing each of the above structures, relates to a method of manufacturing a semiconductor device comprising at least a wiring on an insulating surface, characterized in that the wiring is formed by steps of forming a tungsten film by a sputtering method and patterning the tungsten film.
In the above structure, the sputtering method is characterized in that a tungsten target having a purity of 4N or more is used.
In the above structure, the sputtering method is characterized by using a tungsten alloy target having a purity of 4N or more.
In the above structure, the sputtering method is characterized by using only argon as a sputtering gas.
Further, in each of the above structures, it is possible to obtain the desired value of film stress within the range of xe2x88x922xc3x971010 dyn/cm2 to 2xc3x971010 dyn/cm2, preferably, xe2x88x921xc3x971010 dyn/cm2 to 1xc3x971010 dyn/cm2 by properly controlling substrate temperature, gas pressure, and sputtering power.
Further, the sputtering method is characterized in that it is performed at a substrate temperature of 300xc2x0 C. or less and also, at a gas pressure from 0.1 Pa to 3.0 Pa, preferably, from 1.0 Pa to 2.0 Pa.
Still further, the sputtering method is characterized in that the sputtering power is 300 W to 15 KW, preferably, 1 KW to 9 KW (target having the size of xcfx86305 mm), namely, in the sputtering power par unit area, 0.41 W/cm2 to 20.53 W/cm2, preferably, 1.37 W/cm2 to 12.32 W/cm2.
Note that, in this specification, as shown in FIG. 28, the term xe2x80x9cinternal stressxe2x80x9d is referred to as a tensile stress and denoted by the symbol xe2x80x9c+xe2x80x9d as a stress in the direction of plus when a thin film 51 contracts with respect to a substrate 52, and the substrate 52 is pulled in a direction to prevent the contraction and the thin film 51 changes shape on the inside. On the other hand, when the thin film 51 expands, the substrate 52 is pushed shorter and the thin film 51 changes shape on the outside, and therefore this is referred to as compressive stress and denoted by the symbol xe2x80x9cxe2x88x92xe2x80x9d as a stress in the direction of minus.
Also in this specification, the term xe2x80x9celectrodexe2x80x9d refers to a portion of the xe2x80x9cwiringxe2x80x9d, and denotes a location for performing electrical connection to another wiring, or a location intersection with a semiconductor layer. Therefore, for convenience of explanation, while the use of xe2x80x9cwiringxe2x80x9d and xe2x80x9celectrodexe2x80x9d is properly divided, xe2x80x9cwiringxe2x80x9d can be regarded as being included in xe2x80x9celectrodexe2x80x9d.
The embodiment modes of the present invention is explained below.
In order to solve the above stated problems, the present invention provides a high melting point metallic film obtained by sputtering using a target made from a high melting point metal having high purity. The typical use of tungsten (W) as the high melting point metal is one characteristic of the present invention.
A tungsten target having a high purity of 4N (99.99%) or more, preferably 6N (99.9999%) or more, is used as the target, and simple argon (Ar) gas is used as a sputtering gas.
Further, one characteristic of the present invention is that by regulating the substrate temperature and the sputtering gas pressure (gas pressure), stress control is performed. By setting the substrate temperature of 300xc2x0 C. or lower, and by setting the sputtering gas pressure from 1.0 Pa to 3.0 Pa, preferably between 1.0 Pa and 2.0 Pa, the film stress can be placed from xe2x88x925xc3x971010 dyn/cm2 to 5xc3x971010 dyn/cm2, preferably between xe2x88x922xc3x971010 dyn/cm2 and 2xc3x971010 dyn/cm2, more preferably between xe2x88x921xc3x971010 dyn/cm2 and 1xc3x971010 dyn/cm2.
Further, one characteristic of the present invention is that stress control is performed by regulating the substrate temperature, the sputtering gas pressure (gas pressure), or sputtering power.
Also, conventionally, if the sputtering power is made large, the film stress increases. However, by utilizing the present invention as stated above, the increase of film stress can be repressed and a large sputtering power can be introduced, thereby improving the sputtering rate.
The sodium (Na) concentration and the potassium (K) concentration of a tungsten film obtained in accordance with the above stated sputtering method was analyzed by a GDMS analysis method. The results of the analysis are shown in Table 1 and in FIG. 25.
Note that GDMS analysis is an abbreviation for the Glow Discharge Mass Spectrometry method in this specification, and is a solid state mass spectrometry method which sputters and ionizes a test piece by glow discharge. By obtaining a stable ion source, GDMS analysis is enjoying widespread use as a microanalysis method.
As shown in Table 1 and in FIG. 25, the concentration of sodium (Na) in the tungsten film can be made of 0.3 ppm or less, preferably 0.1 ppm or less. If the film is used as a gate wiring, the sodium (Na) concentration can be kept within a range at which it does not impart any influence to the TFT characteristics. When a large concentration of sodium (Na) is contained within a gate electrode, there is a harmful influence imparted to the TFT characteristics.
Further, the wiring of a semiconductor device may be made into a lamination structure of the tungsten film and a nitrated tungsten film. For example, after depositing tungsten nitride (WNx, where 0 less than x less than 1) on an insulating surface, tungsten (W) is laminated. In order to increase the adhesion, a structure in which a silicon film having conductivity (for example, a phosphorous-doped silicon film or a boron-doped silicon film) is formed on underlayer of the tungsten nitride (WNx) may be used. Note that the wiring can be formed with a line width of 5 xcexcm or less, and a film thickness from 0.1 to 0.7 xcexcm.
The stress values for the tungsten film of the present invention are shown in FIG. 26(a), the stress values after heat treatment (for 4 hours at 500xc2x0 C.) are shown in FIG. 26(b), and the stress values after heat treatment (for 4 hours at 800xc2x0 C.) are shown in FIG. 26(c). The film deposition conditions for the tungsten film are as follows: an argon gas flow rate set to 100 sccm, and a sputtering power set to 6 kW. Note that in FIG. 26(b) and FIG. 26(c), a silicon oxide nitride film having a thickness of 200 nm (SiOxNy, where 0 less than x, and y less than 1) covers the tungsten film during heat treatment.
The tungsten film of the present invention is a film which has an initial tensile stress as the heat treatment temperature increases, but if heat treatment is performed, there is a tendency for the tensile stress to increase further, and therefore control of the film stress can be easily performed.
Note that the stress of the tungsten film of the present invention can be controlled by the substrate temperature, the pressure, and the sputtering power at the time of film deposition. Transition of the tungsten film stress after annealing differs from whether or not a silicon nitride oxide film is formed covering the tungsten film. Namely when the tungsten film is covered by the silicon nitride oxide film, the stress changes in the tensile direction after annealing, and when the tungsten film is not covered by the silicon nitride oxide film, the stress changes in the compressive direction. If the condition for depositing the tungsten film are adjusted to give the tungsten film a weak compressive stress for cases in which it is covered by the silicon nitride oxide film, and to give the tungsten film a weak tensile stress for cases in which it is not covered by the silicon nitride oxide film, then it is possible to reduce the stress after annealing.
Furthermore, FIG. 30 is a graph showing the relationship between sputtering power and stress. The stress of the tungsten film (having a film thickness of 400 nm) before and after heat treatment (for 4 hours at 550xc2x0 C.) is shown in FIG. 30, respectively. It is thus possible to easily regulate the stress in accordance with the sputtering power. Also, as shown in FIG. 31, when the sputtering power is changed the resistivity is also changed. FIG. 31 shows that the resistivity of the tungsten film before and after heat treatment (for 4 hours at 550xc2x0 C.), respectively. The data of sputtering power shown in FIGS. 30 and 31 is obtained by using a target having the size of xcfx86305 mm. Therefore. it is needless to say that the data can be converted to sputtering power par unit area.
Further, as a comparative example of general high melting point metal, FIG. 26(a) shows the pressure value of a lamination film of tantalum and tantalum nitride, FIG. 26(b) shows the pressure value after heat treatment (for 4 hours at 500xc2x0 C.), FIG. 26(c) shows the pressure value after heat treatment (for 4 hours at 800xc2x0 C.). In the same way, in FIG. 26(b) and FIG. 26(c), a silicon oxide nitride film having a thickness of 200 nm (SiOxNy, where 0 less than x, and y less than 1) covers the tungsten film during heat treatment.
As shown in FIG. 26(a) to FIG. 26(c), a lamination film of tantalum and tantalum nitride is a film which has an initial tensile stress as the heat treatment temperature increases, but if the heat treatment is performed, there is a tendency that the lamination film is transferred into the film having the compression pressure and therefore it is difficult to control the film stress.
Further, the resistivity of the tungsten film of the present invention is shown in FIG. 27(a), the resistivity after heat treatment (for 4 hours at 500xc2x0 C.) is shown in FIG. 27(b), and the resistivity after heat treatment (for 4 hours at 800xc2x0 C.) is shown in FIG. 27(c). Note that the resistivity here refers to the electrical resistivity.
As shown in FIGS. 27(a) to 27(c), the tungsten film of the present invention has a low resistivity (about 12 to 16 xcexcxcexa9xc2x7cm), and almost no change in resistivity can be seen after heat treatment. Note that it is possible to make the resistivity of a tungsten film 12 xcexcxcexa9xc2x7cm or less, preferably around 9 xcexcxcexa9xc2x7cm by appropriately changing the sputtering conditions.
On the other hand, general high melting point metals do not have tolerance to oxidation, and is easily oxidized by heat treatment in an atmosphere in which several ppm of residual oxygen exists. As a result, the electrical resistivity increases and film peeling occurs. Further, the electrical resistivity also increases by impurity elements, such as a microscopic amount of oxygen contained in the reactive gas, being injected into the high melting point metallic film, during ion doping.
For example, although a lamination film of tantalum and tantalum nitride is covered by a 200 nm thick silicon nitride oxide film SiOxNy (where 0 less than x, and y less than 1) when heat treatment is performed thereon, there is an increase in resistivity after heat treatment (about 50 to 80 xcexcxcexa9xc2x7cm) by several times in comparison to that before heat treatment (about 25 xcexcxcexa9xc2x7cm)
Furthermore, in the cases of forming a contact with another conducting film, an etching treatment is normally performed for removing a thin oxide film and contaminants before formation of the other conducting film. Next, the results of performing a comparison of resistance values, depending upon whether heat treatment is performed or not (for 1 hour at 500xc2x0 C.), and whether etching (using {fraction (1/10)} diluted HF) is performed or not before film deposition of an electrode 62 (Alxe2x80x94Si (2 wt %)), during formation of the structure shown in FIG. 29 on a substrate 60, are shown in Table 2.
Note that the number of contacts is set to 50, the total contact surface area is about 420 xcexcm2, and a comparison is performed between an electrode having a lamination structure of tantalum and tantalum nitride and an electrode having a lamination structure of the tungsten film and the tungsten nitride film. Note also that resistance values per 1 xcexcmxe2x96xa1 of contact surface area are shown in Table 2. The resistance value per 1 xcexcmxe2x96xa1 of contact surface area is referred to contact resistance values here.
The contact resistance between an electrode 61 having a lamination structure of tantalum and tantalum nitride and the electrode 62 (Alxe2x80x94Si (2 wt %)) is lower for the case when etching (using {fraction (1/10)} diluted HF) is performed than for the case when etching is not performed. Further, when heat treatment is performed, a rapid increase is seen in the contact resistance of the wiring having the lamination structure of tantalum and tantalum nitride, and the value reaches 0.4 kxcexa9.
On the other hand, there is no change seen in the contact resistance between the electrode 61 having a lamination structure of the tungsten film and the tungsten nitride film and the electrode 62 (Alxe2x80x94Si (2 wt %)) depending upon whether heat treatment or etching (using {fraction (1/10)} diluted HF) is performed or not. The contact resistance value of this specification shows a sufficiently low resistance value of 1.3 xcexa9. Provided that this resistance value of the contact is 40 xcexa9 or less, preferably 10 xcexa9 or less, more preferably 5 xcexa9 or less, it is possible to use the tungsten film as a wiring. Furthermore, the film is not covered by the silicon nitride oxide film, similar to FIG. 2, when the heat treatment of Table 2 is performed.
In other words, there is almost no change in the resistivity of the tungsten film of the present invention when heat treatment is performed, even when not covered bv a film such as the silicon nitride oxide film. It is thus understood that the tungsten film of the present invention has an extremely high resistance to heat, and that it is difficult to oxidize the film. Further, it is possible to omit etching for cases of using the tungsten film of the present invention.
By using the tungsten film, in which the amount of sodium contained within the film is 0.03 ppm or less, which has a low electrical resistivity (40 xcexcxcexa9xc2x7cm or less) even after heat treatment, and in which the stress is controlled to be from xe2x88x925xc3x971010 to 5xc3x971010 dyn/cm2, preferably, xe2x88x921xc3x971010 to 1xc3x971010 dyn/cm2 as the material for the gate wirings and other wirings of the TFT, the present invention can greatly increase the operating performance and the reliability of a semiconductor device provided with the TFT.